What you Need to Know about UV Filters

The discussion about using or not using an UV filter for a DSLR is in a state of stall. Some very good photographers hate the filters and some very good photographers always use them. We won’t try to take a side in this article, just provide some tidbits of information that will help you decide if you need to use an UV filter and when.

Any Filter Degrades Image Quality

This is a physical fact, anything you put between your scene and the camera sensor will affect the final IQ of the image. Better and more expensive filters have a lesser impact than cheap filters. If the IQ degradation is noticeable or not and if that is justified or not depends on the conditions you are shooting and the photographer’s quality standards.

UV Light has almost no impact on a DSLR

UV light used to be a problem with film and that’s why UV filters were created, that was a long time ago. Today most DSLR sensors can’t be affected by daytime UV radiation so the UV filter only works as a neutral protective filter in a modern camera. For a DSLR an UV filter and a protector filter are exactly the same thing.

The Camera Front Element is Stronger than what you Think

For almost all lenses the front element is a thick piece of solid glass, breaking it takes a lot of force and the lenses are also hard to scratch, if you have an unfortunate encounter with a force strong enough to break or scratch your front element then the UV filter will probably not help.

Flares, Reflections, Refractions

When you use a filter, UV, polarizer or any filter you add a new optical layer where light can be reflected and refracted. If you shoot at night or if you are in front of your light source the filter can cause flares and reduce the IQ of your shot. This holds for any filter, not only UV filters.

UV Filters are Thin

It’s very easy to break an UV filter, as they are made by a very thin layer of glass. If the filter breaks it can shatter and damage/scratch the front element of your lens. This is something to think about as you can get a problem where you didn’t have one.

Focal Length and Aperture are Important

For some lenses only a small part of a filter is really visible to the light entering the sensor. The formula is simple:

Focal_Length / Max Aperture = filter_surface used

As an example, for a 17mm F4 lens 17/4 = 4.25mm then if you use a 67mm filter only a small part of the filter is used. For a 200mm F2.8 lens we have 200/2.8 = 71.4 if the lens uses a 77mm filter then almost all the filter is used. This is important because you need a high quality filter if a large part of it is used as any difference in the optical surface will affect image quality. In conclusion: for telephoto lenses and very fast lenses you need very high quality filters or no filters at all.

Slim vs Non-Slim filters

Slim filters have a smaller profile and are used to prevent vignetting. Those are useful in wide or ultra-wide angle lenses. The disadvantage of slim filters is that as the support frame is smaller they are more likely to bend and have microscopical variations on its surface. For telephoto lenses use non-slim high quality filters.

Dust, Water Spray and Condensation

In situations where the air is very dusty or very humid or when water can spray your camera a filter can be a big help. If you need to constantly wipe the lens it’s better to wipe the filter. And in the case of dust it can be very abrasive sometimes so you want to avoid scratching your lens while attempting to clean it.

Michael

Vipul Rege

Kurt

Good and insightful, thanks. What about the vacuum effect when using autofocus? My understanding has been that dust being pulled inside the lens by the movement if the elements of the lens is a very real risk, and that the screwed on filter helped to protect against this issue. My question has always been, why don’t the lens manufacturers provide a filter in this case? Is the vacuum effect therefore just an urban myth?